Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16J—PISTONS; CYLINDERS; SEALINGS
  • F16J15/00—Sealings
  • F16J15/16—Sealings between relatively-moving surfaces
  • F16J15/34—Sealings between relatively-moving surfaces with slip-ring pressed against a more or less radial face on one member
  • F16J15/3404—Sealings between relatively-moving surfaces with slip-ring pressed against a more or less radial face on one member and characterised by parts or details relating to lubrication, cooling or venting of the seal

Definitions

• This invention relates to a seal assembly for a rotary machine and more particularly to a seal assembly adjacent to a bearing compartment of such a machine which blocks the entry of hot working medium gases into the bearing compartment and loss of lubricating fluid from the bearing compartment.
• An axial flow rotary machine such as a gas turbine engine for an aircraft, includes a compression section, a combustion section and a turbine section.
• a flow path for hot working medium gases extends axially through the sections of the engine.
• the flow path for hot gases is generally annular in shape.
• the gases are compressed in the compression section causing the temperature and pressure of the gases to rise.
• the hot, pressurized gases are burned with fuel in the combustion section to add energy to the gases. These gases are expanded through the turbine section to produce useful work and thrust.
• the engine has a rotor assembly in the turbine section which is adapted by a rotor disk and blades which extend outwardly therefrom to receive energy from the hot working medium gases.
• the rotor assembly extends to the compression section.
• the rotor assembly has compressor blades extending outwardly across the working medium flow path.
• the high energy working medium gases in the turbine section drive the rotor assembly about its axis of rotation.
• the compressor blades rotate with the rotor assembly and drive the incoming working medium gases rearwardly, compressing and heating the gases ⁇ H ⁇ prior to the gases entering £. ⁇ ' ⁇ the combustion chamber.
• the stator assembly includes a plurality of bearing compartments. Each bearing compartment has at least one bearing for supporting the rotating shaft of the rotor assembly from the stator assembly.
• the bearing in the bearing compartment is supplied with a lubricating fluid, such as oil, for lubricating its surfaces.
• a seal assembly extends between the rotating shaft and the bearing compartment to block the leakage of oil from the bearing compartment and the leakage of hot working medium gases into the bearing compartment.
• seal assembly for such a bearing compartment is shown in U.S. Patent 4,406,459 issued to Davis and Sidat entitled "Oil Weepage Return for Carbon Seal Plates" which is assigned to the assignee of this application.
• the seal assembly has a seal plate which is rotatably attached to the rotor shaft.
• a seal element typically formed of carbon, is supported by the stator assembly and is urged against the seal plate to block the leakage of oil out of the compartment and the leakage of working medium gases into the compartment. Oil is supplied to the location of abutting contact between the seal plate the seal element to lubricate these rubbing surfaces.
• Oil supplied to these surfaces may flow from the seal assembly out into the region between the seal assembly and the rotor shaft.
• An oil return passage 58 in the seal plate provides a conduit for returning the oil to the bearing compartment. Rotation of the seal plate about the axis of the engine exerts a radial force on oil in the return passage and forces the oil radially outwardly through the passages.
• oil leaking from the bearing compartment will migrate through cavities between the rotor shaft and the seal element into the interior of the engine.
• the oil may reach a location where it accumulates in insulation or is trapped in other areas of the engine. This creates a potential for fires should the oil come in contact with hot working medium gases which contain oxygen and remain there at a high enough temperature for a sufficient length of time to cause ignition.
• This invention is predicated in part on the recognition that rotational movement of the shaft about its axis of rotation will energize boundary layers adjacent the surfaces on the shaft and on elements attached to the shaft. These energized boundary layers may be employed to force oil which has leaked from the bearing compartment back toward the bearing compartment and, in constructions that have oil return holes, back to the oil return holes.
• a seal assembly for an oil containing compartment in an axial flow rotary machine adjacent to an annular chamber includes an annular gap between adjacent surfaces of the rotor and the stator which is in close proximity to the annular chamber, which is bounded by a rotating surface, and which has at least one of the bounding surfaces being outwardly tapered toward the chamber to pressurize the chamber.
• the stator has a second surface which bounds the annular clearance gap, which is spaced from the rotating surface by a predetermined distance which is less than one-sixteenth of the radial distance from the axis of rotation to the annular gap.
• the seal assembly includes an oil return passage which extends from the annular chamber to the bearing compartment and the rotational energy imparted to oil and gases through the boundary layer in the annular gap G drives oil toward the oil return passage.
• a primary feature of the present invention is a seal assembly having two seal faces in rubbing contact at an interface. Another feature is an annular clearance gap between a stationary surface and a rotating surface in close proximity to the interface.
• At least one of the surfaces bounding the gap is outwardly tapered toward the passage.
• the tapered surface may be on the rotating component bounding the gap, the stationary component bounding the gap, or on both components bounding the gap.
• the angle that the surface makes with the axis of rotation is greater than three degrees.
• an oil return passage extends radially through a rotating component to the bearing compartment.
• An annular groove for collecting oil faces radially inwardly.
• a second collection groove is radially inwardly of the first collection groove and faces radially outwardly.
• the rotating compartment has an outwardly tapered surface which extends axially over a portion of the compartment; and, an inwardly tapered surface.
• the inwardly tapered surface extends axially over another portion of the component to bound the outwardly facing groove.
• a principal advantage of the present invention is the integrity of the engine which results from blocking the loss of oil from a compartment by pressurizing the sealing interface. Another advantage is the minimal effect on engine efficiency required to pressurize the sealing interface which results from using an already existing boundary layer to provide a pumping force to pressurize the area adjacent the oil compartment. In one detailed embodiment, an advantage is the effectiveness of an oil return system which results from using both boundary layer forces and the interaction of angled surfaces with the boundary layer to direct the oil to the oil return passages.
• Figure 1 is a simplified cross-sectional view of a bearing compartment for an axial flow rotary machine.
• Figure 2 is an enlarged cross-sectional view of a portion of the components shown in Figure 1.
• Figure 3 is an alternate embodiment of the annular gap shown in Figure 2.
• Figure 4 is an alternate embodiment of the annular gap shown in Figure 2.
• Figure 5 is a diagrammatic illustration of the interaction of the surfaces shown in Figure 2.
• Fig. 1 is a side elevation view of part of an axial flow rotary machine 10.
• Fig. 1 shows a portion of the turbine section 12 of the machine to illustrate one embodiment of the present invention.
• the rotary machine has a stator assembly 14 which extends circumferentially about the engine.
• a rotor assembly, as represented by the rotor shaft 16, includes rotor blades (not shown) .
• the rotor shaft has an axis of rotation Ar.
• the rotor blades are adapted to extend radially outwardly across a flow path for hot, working medium gases (not shown) in the compression section (not shown) and the turbine section.
• Working medium gases are flowable from the working medium flow path in the compression section, as shown by the path 18, to provide cooling air to the turbine section. These gases are relatively hot compared to ambient temperature, but are relatively cool compared to the high temperatures of the turbine section.
• the stator assembly 14 includes a bearing compartment 22 having walls 24, 26.
• a bearing 28 for rotatably supporting the shaft 16 is disposed in the bearing compartment.
• An annular support 32 for the bearing extends inwardly through the walls.
• At least a portion of the wall 24 has insulation 34 disposed about the bearing compartment. The insulation blocks the transfer of heat to the bearing compartment from the hot working medium gases 18.
• a shield 36 extends circumferentially about the insulation to shield the insulation from contaminants, such as migrating oil, on the interior of the engine.
• An oil supply passage 38 extends inwardly of the bearing and is in flow communication with a source of pressurized oil (not shown) via an annular passage 42.
• the oil supply passage is in flow communication with passages through the inner race 44 (not shown) of the bearing assembly to lubricate the bearing 28 and other rotating components.
• the bearing compartment 22 contains oil and oil vapors.
• a seal assembly 46 is provided to the shaft 16 and to the bearing compartment 22 to block the leakage of oil from the bearing compartment.
• the seal assembly includes a seal plate 48 rotatable with the shaft and a non-rotatable seal element assembly 52 which slidably engages the seal plate at a first location 54 and slidably engages the bearing compartment as discussed below.
• the bearing compartment 22 has a plurality of axially extending rods 56 and a flange 56 having a pair of annular grooves 62 which face outwardly.
• Each outwardly facing groove carries a circumferentially extending piston ring 64 which extends circumferentially in the groove.
• Each piston ring has a sealing face 66 which adapts the piston ring to slidably engage the seal element assembly.
• the seal element $ assembly ⁇ includes a carbon seal 2 element 68 and a support ring 72 for the carbon seal element which extend about an axis A s .
• the support ring has a circumferentially extending seal land 74 to slidably engage the sealing faces of the piston rings.
• the support ring has a circumferentially extending flange 76.
• the flange has a plurality of holes, as represented by the hole 78 to slidably engage the rods.
• the rotor assembly 16 includes a shaft element, as represented by the spacer 84.
• the spacer extends circumferentially about an axis A s . The spacer abuts the seal plate and is rotatable with the shaft.
• the rotor assembly 16 is adapted by a radially extending flange 92 to engage the sleeve.
• the radially extending flange has a radial height h,.
• the shaft spacer element 84 has a radially extending flange 94 having a radial height h,.
• the radial height h, and the radial height of the sleeve are greater than or equal to the radial height h 2 of the axially extending flange of the shaft element to ensure
• Figure 2 is an enlarged cross sectional view of the shaft spacer element 84, the seal element assembly 52 and the seal plate 48 shown in Figure 1. Relative static pressures as shown by the symbols P-, P+, p and P++.
• the carbon seal element 68 has a seal face 96 and an inwardly facing surface 98.
• the surface is spaced radially from the shaft 16 leaving a circumferentially extending cavity 102 therebetween.
• the surface extends axially in a first axial direction A, toward the seal plate.
• the surface diverges radially outwardly away from the axis of rotation A r and the axis A s in this first axial direction.
• the seal face 96 faces in the first axial direction.
• the seal face extends outwardly from the surface 98 and slidably engages the seal plate 48.
• the rotatable seal which faces in a second first axial direction.
• the seal face slidably engages '/" * the seal face 96 of the seal element 68 at a first location.
• the seal plate 48 has a circumferentially extending annular passage 106 for receiving lubricating oil from the passage 38.
• the seal plate 48 has a second face 112 which extends radially inward from the first location.
• the second face is spaced axially from the seal element 68 leaving a annular groove 114 therebetween.
• the annular groove faces radially inwardly.
• At least one oil return passage 116 extends radially outwardly from the annular groove through the seal plate and to the bearing compartment. The oil return passage places the bearing compartment in flow communication with the inwardly facing groove.
• the spacer 84 has an outwardly facing first surface 118.
• the outwardly facing surface extends toward the first location in the first axial direction.
• the first surface diverges outwardly in that direction from the axis A s and from the axis of rotation A p .
• the outwardly facing first surface is spaced radially from the inwardly facing surface of the seal element leaving a clearance gap G therebetween.
• the spacer 84 has an outwardly facing second surface 122.
• the outwardly facing second surface extends convergently from the first surface in the first axial direction toward the shaft 16 and to the second radially extending surface 112 of the seal plate 48.
• the outwardly facing second surface is spaced axially from the seal plate over at least a portion of the second surface leaving an outwardly facing groove 124 therebetween.
• the groove is bounded by the seal plate and the spacer element.
• the outwardly facing groove and the inwardly facing groove bound an annular chamber 126.
• the annular chamber is in flow communication with the annular clearance gap G between the seal element 68 and the spacer.
• Fig. 3 is an alternate embodiment of the construction shown in Figure 2 having a cylindrical surface 128 on the rotating shaft spacer element 84 and a frusto-conical surface 132 on the inwardly facing surface of the carbon seal element 68.
• Figure 4 is an alternate embodiment of the construction shown in Figure 3 having a frusto-conical divergent first surface 134 on the shaft spacer element and a cylindrical inwardly facing surface on the carbon ⁇ seal element 68.
• Figure 5 is a schematic representation, enlarged and not to scale showing the relationship of the outwardly facing first surface 118 on the shaft spacer element to the inwardly facing surface 98 on the carbon seal element 68.
• the circumferentially extending boundary layer is shown by the arrows, with the direction of the arrows reflecting the mechanical interaction of the inclined surface 98 on the carbon seal element with the boundary layer.
• the rotor assembly 16 rotates about the axis of rotation A at minimum speeds that exceed five thousand revolutions per minute.
• the bearing 28 engages the shaft and permits rotational movement of the shaft with respect to the stator assembly. Oil is flowed to the bearing compartment 22 to cool the rotating components and to lubricate critical components such as the bearings.
• the seal plate 48 and carbon seal element 68 are two other components that require lubrication.
• Lubricating oil is flowed from the annular passage 106 radially outward via passage 108 through the rotating seal plate. As the oil is flowed outwardly, rotational forces exerted by the seal plate on the oil force the oil to the sealing interface at the first location between the seal plate and the carbon seal element. A portion of the oil supplied to the interface returns immediately to the bearing compartment 22 by flowing outwardly. Another portion of the oil flows radially inwardly into the outwardly facing annular groove 114. It is believed that the oil may enter with such velocity that it is propelled radially inwardly past the annular clearance gap G and against the second surface 122 of the spacer.
• a portion of the oil may be urged toward the clearance gap G between the seal element 68 and the spacer 84.
• the first surface 118 travels circumferentially about the axis of rotation A r at high velocities.
• the high velocity of the first surface creates an energized boundary layer which extends outwardly to the outwardly tapered stationary surface 98 on the seal element.
• the boundary layer and any oil trapped in the boundary layer are forced against this inclined surface.
• the inclined surface directs the oil toward the annular chamber by mechanical interaction with the oil and by mechanically directing the energized boundary layer in that direction.
• the clearance gap G is selected to be small enough to provide the pumping action to the oil which is required to return the oil to the annular chamber. There is another constraint on the size of the gap.
• the rotor assembly 16 moves radially outwardly and moves axially with respect to the stationary outer surface 98 in response to rotational forces and changes in operating temperatures. Accordingly, the clearance gap is selected to at least take into account these axial and radial movements.
• the boundary layer is much larger than the annular gap and its approximate size may be calculated from equations for flat plate theory set forth in Viscous Fluid Flow (2nd Ed.) by F. M. White published by McGraw Hill, Inc. (New York 1991) at page 235 and introduction to Fluid Mechanics, (3rd Ed.) by Fox and McDonald published by John Wiley and Sons (New York 1985) at page 448.
• the optimum gap may be determined empirically.
• a radial gap has a radial height which is less than or equal to one sixteenth of the radial distance from the axis of rotation to the radial gap, (that is, the radial height of the clearance gap G is normalized by the radius R to the gap) .
• the innermost portion of the first surface 118 travels at a much lower circum ⁇ ferential velocity than the outermost portion of the first surface.
• the groove 124 adjacent the face 112 of the seal plate and the convergent second surface 124 of the spacer 84 has a higher circumferential velocity at the radially inward portion P- than adjacent the stationary carbon seal element (P++) , causing a static pressure gradient which urges the oil towards the face 112 of the rotating seal plate.
• the oil is mechanically directed towards this face by the angled second surface 124 which faces the surface 112 of the seal plate.
• the construction shown in Fig. 3 has the first beneficial effect of the construction Fig. 2, that is, mechanically urging the oil and the energized boundary layer toward the annular chamber 126.
• the construction shown in Fig. 4 has the second beneficial effect of the construction shown in Fig. 2, that is, creating a static pressure gradient which acts to block the loss of oil.
• creating a static pressure gradient which acts to block the loss of oil.
• preventing the oil from moving through the radial gap into other regions of the engine has beneficial results. For example, should the oil enter the insulation 34 surrounding the bearing compartment, it could provide both a source of combustible material and degrade the insulating performance of the insulation resulting in higher bearing temperatures and possible combustion in the bearing area.
• the end of the spacer 84 has ⁇ a radial height h 2 which is equal to the height h, 'radial projection on the £ " - shaft which receives the axial load transmitted from the spacer element via the labyrinth seal element to the radial projection. This avoids any bending moments from being imposed on the sleeve element which would occur if the spacer element extended radially beyond the radial projection in the shaft.

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• Engineering & Computer Science (AREA)
• General Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Sealing Using Fluids, Sealing Without Contact, And Removal Of Oil (AREA)

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Publications (1)

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• 1993
  • 1993-07-09 EP EP93917088A patent/EP0685048B1/de not_active Expired - Lifetime
  • 1993-07-09 JP JP50625194A patent/JP3555683B2/ja not_active Expired - Lifetime
  • 1993-07-09 WO PCT/US1993/006503 patent/WO1994004856A1/en active IP Right Grant
  • 1993-07-09 DE DE69327665T patent/DE69327665T2/de not_active Expired - Lifetime
• 1994
  • 1994-06-20 US US08/263,155 patent/US5464227A/en not_active Expired - Lifetime

Patent Citations (4)

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